Ever since the first clinical reports of patients with AIDS in 1981, there have been improvements both in the knowledge base of the pathogenesis of HIV in causing AIDS as well as a progressive refinement in the test methodologies used to diagnose this illness.1-3 Given that there are both public health and clinical benefits in earlier diagnosis and treatment of patients with available antiretroviral therapies, universal screening with opt-out consent has been a standard of practice recommendation by the Centers of Disease Control and Prevention (CDC) since 2006; universal screening with opt-out consent also has been recommended by the US Preventative Task Force and has been widely implemented.4-7
HIV Screening
While HIV screening assays have evolved to be accurate with very high sensitivities and specificities, false-positive results are a significant issue both currently and historically.8-16 The use of an HIV assay on a low prevalence population predictably reduces the positive predictive value (PPV) of even an otherwise accurate assay.8-23 In light of this, laboratory HIV testing algorithms include confirmatory testing to increase the likelihood that the correct diagnosis is being rendered.
The fourth-generation assay has been shown to be more sensitive and specific compared with that of the third-generation assay due to the addition of detection of p24 antigen and the refinement of the antigenic targets for the antibody detection.6,8,11-13,18-20,22 Due to these improvements, in the general population, increased sensitivity/specificity with a reduction in both false positives and false negatives have been reported.
It has been observed in the nonveteran population that switching from the older third-generation to a more sensitive and specific fourth-generation HIV screening assay has reduced the false-positive screening rate.18,19,22 For instance, Muthukumar and colleagues demonstrated a false-positive rate of only 2 out of 99 (2%) tested specimens for the fourth-generation ARCHITECT HIV Ag/Ab Combo assay vs 9 out of 99 tested specimens (9%) for the third-generation ADVIA Centaur HIV 1/O/2 Enhanced assay.18 In addition, it has been noted that fourth-generation HIV screening assays can reduce the window period by detecting HIV infection sooner after initial acute infection.19 Mitchell and colleagues demonstrated even highly specific fourth-generation HIV assays with specificities estimated at 99.7% can have PPVs as low as 25.0% if used in a population of low HIV prevalence (such as a 0.1% prevalence population).19 However, the veteran population has been documented to differ significantly on a number of population variables, including severity of disease and susceptibility to infections, and as a result extrapolation of these data from the general population may be limited.24-26 To our knowledge, this article represents the first study directly examining the reduction in false-positive results with the switch to a fourth-generation HIV generation assay from a third-generation assay for the veteran patient population at a regional US Department of Veterans Affairs (VA) medical center (VAMC).8,11
Methods
Quality assurance documents on test volume were retrospectively reviewed to obtain the number of HIV screening tests that were performed by the laboratory at the Corporal Michael J. Crescenz VAMC (CMJCVAMC) in Philadelphia, Pennsylvania, between March 1, 2016 and February 28, 2017, prior to implementation of the fourth-generation assay. The study also include results from the first year of use of the fourth-generation assay (March 1, 2017 to February 28, 2018). In addition, paper quality assurance records of all positive screening results during those periods were reviewed and manually counted for the abstract presentation of these data.
For assurance of accuracy, a search of all HIV testing assays using Veterans Health Information Systems and Technology Architecture and FileMan also was performed, and the results were compared to records in the Computerized Patient Record System (CPRS). Any discrepancies in the numbers of test results generated by both searches were investigated, and data for the manuscript were derived from records associating tests with particular patients. Only results from patient samples were considered for the electronic search. Quality samples that did not correspond to a true patient as identified in CPRS or same time patient sample duplicates were excluded from the calculations. Basic demographic data (age, ethnicity, and gender) were obtained from this FileMan search. The third-generation assay was the Ortho-Clinical Diagnostics Vitros, and the fourth-generation assay was the Abbott Architect.
To interpret the true HIV result of each sample with a reactive or positive screening result, the CDC laboratory HIV testing algorithm was followed and reviewed with a clinical pathologist or microbiologist director.12,13 All specimens interpreted as HIV positive by the pathologist or microbiologist director were discussed with the clinical health care provider at the time of the test with results added to CPRS after all testing was complete and discussions had taken place. All initially reactive specimens (confirmed with retesting in duplicate on the screening platform with at least 1 repeat reactive result) were further tested with the Bio-Rad Geenius HIV 1/2 Supplemental Assay, which screens for both HIV-1 and HIV-2 antibodies. Specimens with reactive results by this supplemental assay were interpreted as positive for HIV based on the CDC laboratory HIV testing algorithm. Specimens with negative or indeterminant results by the supplemental assay then underwent HIV-1 nucleic acid testing (NAT) using the Roche Diagnostics COBAS AmpliPrep/COBAS TaqMan HIV-1 Test v2.0. Specimens with viral load detected on NAT were positive for HIV infection, while specimens with viral load not detected on NAT testing were interpreted as negative for HIV-1 infection. Although there were no HIV-2 positive or indeterminant specimens during the study period, HIV-2 reactivity also would have been interpreted per the CDC laboratory HIV testing algorithm. Specimens with inadequate volume to complete all testing steps would be interpreted as indeterminant for HIV with request for additional specimen to complete testing. All testing platforms used for HIV testing in the laboratory had been properly validated prior to use.
The number of false positives and indeterminant results was tabulated in Microsoft Excel by month throughout the study period alongside the total number of HIV screening tests performed. Statistical analyses to verify statistical significance was performed by 1-tailed homoscedastic t test calculation using Excel.